Recently, there has been a great interest in chemical vapor deposition of copper metal thin films. Because of its low resistivity, .about.1.7 .mu..OMEGA..multidot.cm, and high electromigration resistance, copper metal thin film material is considered to be ideal for use as metal interconnections in integrated circuits.
Chemical vapor deposition (CVD) of copper requires the use of a stable yet volatile precursor. For the purpose of commercialization, the cost of the copper precursor is an issue. In addition, the copper precursor must have good adhesion to metal nitride coated substrates, low resistivity, .about.1.8 .mu..OMEGA..multidot.cm, excellent conformity to surface structures, and good electromigration resistance. In CVD processes, generally performed at elevated temperatures, the copper precursor must have a vapor pressure high enough to achieve a reasonable deposition rate, and must also be stable at deposition temperatures, without any decomposition in the CVD liquid delivery line or during vaporizer.
Copper metal thin films may be prepared via chemical vapor deposition using a variety of copper precursors. In 1990, D. B. Beach et al., Low-Temperature Chemical Vapor Deposition of High Purity Copper from an Organometallic Source, Chem. Mater. (2) 216 (1990), obtained pure copper films via CVD by using (.eta..sup.5 -C.sub.5 H.sub.5)Cu(PMe.sub.3). At about the same time, Hampden-Smith, M. J. et al., Chem. Mater. (2) 636 (1990) declared the same results by using (tert-BuO)Cu(PMe.sub.3). These copper films, however, contain carbon and phosphorus, which elements constitute contaminants when used as interconnections in integrated circuits, and so they cannot be used as interconnectors in microprocessors. The studies of copper precursors conducted in the early of 1990's were concentrated on the evaluation of a series of copper(I) fluorinated .beta.-diketonate complexes, which have been proven to be very promising sources for the use in the chemical vapor deposition of copper metal thin films.
Copper(I) fluorinated .beta.-diketonate complexes were synthesized by Gerald Doyle, as described in U.S. Pat. No. 4,385,005, granted May 24, 1983, for Process for separating unsaturated hydrocarbons using copper or silver complexes with fluorinated diketonates, and U.S. Pat. No. 4,425,281, granted Jan. 10, 1984, for Copper or silver complexes with fluorinated diketones and unsaturated ligands, in which he presented the synthesis method and its application in the separation of unsaturated organic hydrocarbons.
U.S. Pat. No. 5,096,737, to Baum et al., granted Mar. 17, 1992, for Ligand Stabilization +1 Metal Beta-Diketonate Coordination Complexes and Their Use in Chemical Vapor Deposition of Metal Thin Films, described the application of copper(I)fluorinated .beta.-diketonate complexes as copper precursors for CVD copper thin film preparation. Copper thin films have been prepared via chemical vapor deposition using these precursors. Among several liquid copper precursors, 1,5-dimethyl 1,5-cyclooctadiene copper(I)hexafluoroacetylacetonate mixed with 1,6-dimethyl 1,5-cyclooctadiene copper(I)hexafluoroacetylacetonate ((DMCOD)Cu(hfac)) and hexyne copper(I)hexafluoroacetylacetonate ((HYN)Cu(hfac)) were evaluated in detail. The copper thin films deposited using (DMCOD)Cu(hfac) have very good adhesion to metal or metal nitride substrates, but a high resistivity, i.e., .about.2.5 .mu..OMEGA..multidot.cm, and a low deposition rate, whereas by using (HYN)Cu(hfac), the copper film has poor adhesion to a TiN substrate, and high resistivity, i.e., .about.2.1 .mu..OMEGA..multidot.cm.
Another compound, 2-butyne copper(I)(hfac), ((BUY)Cu(hfac)), forms a copper film with low resistivity, .about.1.93 .mu..OMEGA..multidot.cm, but has poor adhesion and is relatively expensive, and, because the compound is a solid, it must be vaporized prior to CVD.
The formation of copper(I)(hfac) stabilized with a series of trialkylvinylsilane (TMVS), as described in U.S. Pat. No. 5,085,731, to Norman et al., granted Feb. 4, 1992, for Volatile liquid precursors for the chemical vapor deposition of copper, results in improved copper thin films. Copper films, deposited using a liquid copper precursor of (hfac)Cu(TMVS) are of low resistivities and are reasonably adhesive to substrates. This liquid copper precursor has been used for the preparation of copper metal thin films via CVD for some time, but still has some drawbacks: stability, the poor adhesion of the copper film, and the cost of the trimethylvinylsilane stabilizer are significant impediments to the widespread use of this technique.
Other references of note are: Gerald Doyle, K. A. Eriksen and D. Van Engen, Organometallics 4, 830 (1985); Thomas H. Baum and Carl E. Larson, Chem. Mater. 4, 365 (1992); and Thomas H. Baum and Carl E. Larson, J. Electrochem. Soc. 140(1), 154 (1993).